Acute respiratory infection is the fourth major cause of morbidity and mortality among under-five children globally. However, the profile of microbial burden that could contribute to these infections among under-five children in the indoor environments has not been extensively studied particularly in developing countries like Nigeria. This study was designed to determine the burden of airborne microbes in indoor environment that predispose under-five children to acute respiratory infections. A prospective case-control design was employed for this study. Two hundred and twenty under-five children each with acute respiratory infection (cases) and without acute respiratory infection (controls) were selected from children visiting Oni-memorial Children Hospital and University College Hospital, Ibadan. A follow-up of 66 consented cases and controls each was carried out to assess the burden of indoor airborne microbes using a non-volumetric method, and the total counts per cubic metre were compared with the American Industrial Hygiene Association guideline. Data were analysed using descriptive statistics, t-test and Spearman's rank correlation. Mean indoor total bacterial count for cases (9.6 Â 10 2 cfu/m 3 ) was significantly higher than the permissible limit recommended by the American Industrial Hygiene Association ( 500 cfu/m 3 ) as compared to controls (3.5 Â 10 2 cfu/m 3 ) (p < 0.05). Educating mothers of under-five children on improved ventilation, good housing and indoor sanitary practices to reduce indoor microbial load is therefore advocated.

Cases were more exposed than controls to environmental risk factors for ARIs. Increased awareness of the importance of environmental factors with regard to prevention and control of ARI is therefore important.

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